Ballasted sequencing batch reactor system and method for treating wastewater

ABSTRACT

A ballasted sequencing batch reactor system for treating wastewater including one or more sequencing batch reactors. A weighting agent impregnation subsystem is configured to mix biological flocs and weighting agent to form weighted biological flocs. A weighting agent recovery subsystem is configured to recover weighting agent from the weighted biological flocs and reintroduce the recovered weighting agent to the weighting agent impregnation subsystem.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 12/584,545, filed Sep. 8, 2009, which is a continuation-in-partof U.S. patent application Ser. No. 12/008,216, filed Jan. 9, 2008, nowU.S. Pat. No. 7,695,623, issued Apr. 13, 2010, which claims benefit ofand priority to U.S. Provisional Application Ser. No. 60/879,373, filedJan. 9, 2007, and U.S. Provisional Application Ser. No. 60/994,553,filed Sep. 20, 2007, all of which are incorporated by reference herein.

FIELD OF THE INVENTION

This invention relates to a ballasted sequencing batch reactor (SBR)system and method for treating wastewater.

BACKGROUND OF THE INVENTION

SBR systems are used to treat wastewater. A typical conventional SBRsystem includes one or more SBRs which contain a large population ofmicroorganisms that ingest contaminants in the influent wastewater toform biological flocs and treat the wastewater. SBR systems typicallyuse four phases to treat wastewater: fill, react, settle, and decant.During the fill phase, the SBR is filled with the influent wastewaterand may be aerated, mixed without aeration, or not mixed and notaerated. The react phase involves adding oxygen, mixing, or acombination thereof, to provide treatment by converting biochemicaloxygen demand (BOD) to microorganisms to form biological flocs. Duringthe settle phase, the biological flocs formed in the previous phases areallowed settle to the bottom of the SBR to form settled sludge. Thedecant phase involves slowly decanting the clear water from the settledsludge to provide a treated effluent.

However, during the settling phase of a typical conventional SBR system,the biological flocs are only marginally heavier than water andtherefore settle very slowly. Moreover, the solids separation in thesettle phase may be unreliable due to many types of settling problemsthat are caused by: overgrowth of filamentous organisms, viscous bulkingcaused by the overgrowth of either zoogleal organisms or exocellularpolysaccharide material, pin floc, straggler floc, and the like. Thismay limit the capacity of a conventional SBR system and can compromisethe quality of the treated effluent.

BRIEF SUMMARY OF THE INVENTION

This invention features a ballasted sequencing batch reactor system fortreating wastewater including one or more sequencing batch reactors. Aweighting agent impregnation subsystem is configured to mix biologicalflocs and weighting agent to form weighted biological flocs. A weightingagent recovery subsystem is configured to recover weighting agent fromthe weighted biological flocs and reintroduce the recovered weightingagent to the weighting agent impregnation subsystem.

In one embodiment, the system may include a sludge storage tankconfigured to receive settled sludge from the one or more sequencingbatch reactors, store the settled sludge therein, and regulate the flowof settled sludge to weighting agent recovery subsystem. The weightingagent recovery subsystem may include a separator subsystem forseparating the weighting agent from the weighted biological flocs. Theseparator subsystem may include a shear mill. The separator subsystemmay include a centrifugal separator. The separator subsystem may includean ultrasonic separator. The separator subsystem may include a shearmill and a wet drum magnetic separator. The separator subsystem mayinclude a shear mill and a centrifugal separator. The separatorsubsystem may include an ultrasonic separator and a wet drum magneticseparator. The separator subsystem may include an ultrasonic separatorand a centrifugal separator. The shear mill may include rotor and astator, wherein the rotor and/or the stator include slots sized as tooptimize separation of weighting agent from the weighted biologicalflocs. The weighting agent impregnation subsystem may include animpregnation tank and at least one mixer. The capacity of the system maybe increased by reducing the duration of a settle phase. The one or moresequencing batch reactors may be configured to decant clear effluentfrom settled sludge to provide a treated effluent. The weightedbiological flocs may enhance the quality of the treated effluent byreducing the concentration of suspended solids and related contaminantstherein. The system may include a wasting subsystem for wasting settledsludge from the weighting agent recovery subsystem to control apopulation of microorganisms in a mixed liquor in the one or moresequencing batch reactors. The capacity of the system may be increasedby increasing the concentration of the mixed liquor in the one or moresequencing batch reactors by reducing the amount of settled sludgewasted by a wasting subsystem. The capacity of the system may beincreased by reducing the duration of a react phase. The amount ofsettled sludge wasted by the wasting subsystem may be reduced toincrease the concentration of mixed liquor suspended solids forenhancing nitrification and/or de-nitrification of ammonia in the mixedliquid. Nitrification may be enhanced by increasing the amount ofdissolved oxygen introduced into the one or more sequencing batchreactors. A coagulant may be added to the one or more sequencing batchreactors for removing phosphorus by precipitation and/or coagulation. Aflocculant may be added to the one or more sequencing batch reactors forenhancing settling and thickening of the weighted biological flocs andfor providing agglomeration of non-impregnated biological flocs and/orpartially impregnated biological flocs with weighted biological flocs.The weighting agent impregnation subsystem may include a venturimixer/eductor. A majority of the weighting agent may have a particlesize less than about 100 μm. A majority of the weighting agent may havea particle size less than about 40 μm. A majority of the weighting agentmay have a particle size less than about 20 μm. The weighting agent mayinclude magnetite. The system may include a mixer disposed in each ofthe one or more sequencing batch reactors for maintaining the suspendedsolids or the mixed liquor in suspension.

This invention also features a method for treating wastewater using oneor more sequencing batch reactors, the method including the steps of: a)receiving influent wastewater in the one or more sequencing batchreactors, b) forming biological flocs in the one or more sequencingbatch reactors, c) impregnating weighting agent into the biologicalflocs to form weighted biological flocs, and d) recovering weightingagent from the weighted biological flocs to reintroduce the weightingagent to step c). In one embodiment, the method may include the step ofseparating the weighting agent from the weighted biological flocs. Themethod may include the step of collecting the weighting agent andrecycling the weighting agent to step c). The method may include thestep of providing weighting agent in which the majority of the weightingagent has a particle size less than about 100 μm. The method may includethe step of providing weighting agent in which the majority of theweighting agent has a particle size less than about 40 μm. The methodmay include the step of providing weighting agent in which the majorityof the weighting agent has a particle size less than about 20 μm. Themethod may include the step of introducing dissolved oxygen to apopulation of microorganisms to promote growth of biological flocs in amixed liquor defined by a concentration of mixed liquor suspendedsolids. The method may include the step of introducing a flocculant tothe mixed liquor to enhance settling and thickening of the weightedbiological flocs and to establish agglomeration of non-impregnatedbiological flocs and/or partially impregnated biological flocs with theweighted biological flocs. The method may include the step of separatingand collecting the weighted biological flocs from the mixed liquor inthe one or more sequencing batch reactors to provide a secondaryeffluent and a settled sludge. The method may include the step ofrecycling the majority of the settled sludge to step b). The method mayinclude the step of decanting the clean effluent from the settled sludgein the one or more sequencing batch reactors to provide a treatedeffluent. The method may include the step of wasting the remainingsettled sludge using a wasting subsystem to control the population ofthe microorganisms in the mixed liquor. The method may include the stepof increasing the capacity of the system by reducing the duration of asettle phase. The method may include the step of enhancing the qualityof the treated effluent by reducing suspended solids and relatedcontaminants therein. The method may include the step of wasting settledsludge from the weighting agent recovery subsystem to control apopulation of microorganisms in a mixed liquor in the one or moresequencing batch reactors. The method may include the step of increasingthe capacity of the system by increasing the concentration of the mixedliquor in the one or more sequencing batch reactors by reducing theamount of settled sludge wasted by a wasting subsystem. The method mayinclude the step of increasing the capacity of the system by reducingthe duration of a react phase. The method may include the step ofreducing the amount of settled sludge wasted by the wasting subsystem toincrease the concentration of mixed liquor suspended solids whichenhances nitrification and/or de-nitrification of ammonia in the mixedliquid. The method may include the step of enhancing nitrification byincreasing the amount of dissolved oxygen introduced into the one ormore sequencing batch reactors. The weighting agent may be impregnatedinto the biological flocs in step b) by mixing the mixed liquor and thebiological flocs at a predetermined energy level.

The subject invention, however, in other embodiments, need not achieveall these objectives and the claims hereof should not be limited tostructures or methods capable of achieving these objectives.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Other objects, features and advantages will occur to those skilled inthe art from the following description of a preferred embodiment and theaccompanying drawings, in which:

FIG. 1 is a schematic block diagram of one embodiment of the SBR systemfor treating wastewater in accordance with this invention;

FIG. 2 is a microscopic view showing one example of weighting agentimpregnated in biological flocs using the weighting agent impregnationsystem shown in FIG. 1;

FIG. 3 is a schematic block diagram showing another embodiment of theSBR system for treating wastewater of this invention;

FIG. 4 is a schematic side-view of another embodiment of theimpregnation subsystem shown in FIGS. 1 and 3;

FIG. 5A is a schematic side-view of one embodiment of the separatorshown in FIGS. 1 and 3;

FIG. 5B is a schematic top view showing one example of slots in therotor and stator of the shear mill shown in FIG. 5A;

FIG. 5C is a three-dimensional view of one embodiment of the shear millin FIG. 5A;

FIG. 6 is a three-dimensional front-view of another embodiment of theseparator shown in FIGS. 1 and 3; and

FIG. 7 is a three-dimensional front-view of yet another embodiment ofthe separator shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

Aside from the preferred embodiment or embodiments disclosed below, thisinvention is capable of other embodiments and of being practiced orbeing carried out in various ways. Thus, it is to be understood that theinvention is not limited in its application to the details ofconstruction and the arrangements of components set forth in thefollowing description or illustrated in the drawings. If only oneembodiment is described herein, the claims hereof are not to be limitedto that embodiment. Moreover, the claims hereof are not to be readrestrictively unless there is clear and convincing evidence manifestinga certain exclusion, restriction, or disclaimer.

There is shown in FIG. 1, one embodiment of SBR system 10 for treatingwastewater of this invention. System 10 includes at least one SBR 12which receives a flow of influent wastewater 14 by line 16. SBR 12preferably introduces air bubbles 18 by line 20 exposed to ambient air22. Air bubbles 18 introduce dissolved oxygen to a population ofmicroorganisms in SBR 12 to promote growth of biological flocs 23 inmixed liquor 24. Mixed liquor 24 as used herein means a combination ofinfluent wastewater 14 and biological flocs 23.

System 10 also includes weighting agent impregnation subsystem 26 which,in one embodiment, includes impregnation tank 28 and mixer 30 whichreceives mixed liquor 24 from SBR 12 by line 32. In one embodiment,impregnation tank 28 preferably receives virgin weighting agent 33,e.g., from feed hopper 34 by line 36, and/or recycled weighting agent 38from weighting agent recovery subsystem 74 (discussed below). Weightingagent impregnation subsystem 26 mixes mixed liquor 24 or settled sludgereceived by line 77 and virgin weighting agent 33 and/or the recycledweighting agent 38 in impregnation tank 28 to impregnate the weightingagent into biological flocs 23 suspended in mixed liquor 24 or settledsludge by line 77 via sludge storage tank 88 and line 76 and/or vialines 76 and 81 to form weighted biological flocs. Mixer 30 utilizes amixing energy which is sufficient to impregnate the weighting agent intobiological flocs suspended in a mixed liquor to form weighted biologicalflocs. FIG. 2 shows one example of weighting agent 33, 38 impregnatedinto biological flocs 23 to form weighted biological flocs 25. Theweighted biological flocs impregnated with the weighting agent are thensent back to SBR 12, FIG. 1, by line 37.

The weighting agent may be magnetite, or any similar type weightingagent or magnetically separable inorganic material known to thoseskilled in the art which increases the density of the biological flocs.In one example, the majority of the weighting agent particles may have asize less than about 100 μm. In other examples, the majority of theweighting agent particles may have a size less than about 40 μm, or, themajority of the weighting agent may have a particle size less than about20 μm.

System 10 also includes weighting agent recovery subsystem 74 whichreceives settled sludge from bottom 39 of SBR 12 by line 76 typicallyafter the settle and decant phases are complete. Weighting agentrecovery subsystem 74 preferably includes separator 78 which recoversthe weighting agent from the weighted biological flocs in the settledsludge in line 76 and reintroduces (recycles) the weighting agent toweighting agent impregnation subsystem 26 by line 79. Weighting agentrecovery subsystem 74 may include recovery subsystem 83, discussedbelow.

In one embodiment, system 10 includes sludge storage tank 88 whichstores settled sludge output from SBR 12 by line 76 typically after thedecant phase is complete.

In one exemplary operation of SBR system 10, SBR 12 is filled withinfluent wastewater 14 via line 16 and seeded with a large population ofmicroorganisms that ingest contaminants in influent wastewater 14 toform biological flocs 23. During a fill phase, dissolved oxygen via airbubbles 18 may be introduced to mixed liquor 24 to promote growth ofbiological flocs 23. Once filled, system 10 undergoes a react phase.

During the fill and/or react phases, weighting agent impregnationsubsystem 26 receives the mixed liquor by line 32, or settled sludge byline 77 via sludge storage tank 88 and line 76 and/or via lines 76 and81, and impregnates the biological flocs therein with virgin weightingagent 33 and/or recycled weighting agent 38 using mixer 30. The mixedliquor or settled sludge having weighted biological flocs is then sentback to SBR 12 by line 37. The react phase is followed by the settlingphase where the weighted biological flocs settle to bottom 39 of SBR 12to form settled sludge. The times for the fill, react, settle, anddecant phases vary as known by those skilled in the art. Then, the cleareffluent is decanted by line 52 to provide treated effluent 50. Duringor after the decant phase, some of the settled sludge at bottom 39 ofSBR 12 may be sent to sludge storage tank 88 via line 76. Sludge storagetank 88 stores sludge from SBR 12 and regulates the flow thereof toweighting agent recovery subsystem 74. Weighting agent recoverysubsystem 74 then recovers the weighting agent from the weightedbiological flocs as discussed above and recycles the weighting agent toweighting agent impregnation subsystem 26 as recovered weighting agent38.

Because the weighted biological flocs in SBR 12 have a greater specificgravity than non-impregnated biological flocs, they settle faster thannon-impregnated biological flocs utilized in a typical conventional SBRsystem. Thus, the time needed for the settling phase of system 10 isreduced. This alleviates settling problems associated with aconventional SBR system, such as overgrowth of filamentous organisms,viscous bulking caused by the overgrowth of either zoogleal organisms orexocellular polysaccharide material, pin floc, straggler floc, and thelike. The result is the capacity of system 10 to treat wastewater may beincreased while providing high quality treated effluent 50.

Because the time needed in the settling phase is reduced, system 10 mayalso allow more time for the react phase, which further increases thequality of treated effluent 50. The weighted biological flocs alsoenhance the quality of the treated effluent by reducing theconcentration of suspended solids and related contaminants therein. Theweighted biological flocs also facilitate higher mixed liquor suspendedsolids (MLSS) concentrations. Operating at higher MLSS concentrationsprovides additional advantages, including additional increased treatmentcapacity, enhanced nitrogen removal, enhanced phosphorus removal, andthe like. Moreover, because weighting agent recovery subsystem 74recovers and recycles the weighting agent, the operational costs ofsystem 10 are significantly reduced.

System 10′, FIG. 3, where like parts have been given like numbers,includes at least two SBRs 12′ and 12″. In this example, SBR 12′ isfilled with influent wastewater 14 by line 16 by opening valve 62 andclosing valve 64. Once SBR 12′ is filled, valve 62 is closed and valve64 is open. SBR 12″ is then similarly filled with influent wastewater14. Thus, system 10′ allows a continuous flow of influent wastewater 14to either SBR 12′ or SBR 12″ for continuous operation. System 10 is notlimited to two SBRs, as any number of SBRs may be utilized toaccommodate the flow rate of influent wastewater 14. In one example,after SBR 12′ is filled and SBR 12″ is in the fill phase, SBR 12′undergoes the react, settle, and decant phases. Similarly, when SBR 12′is in the fill phase, SBR 12″ typically undergoes the react, settle, anddecant phases.

System 10′ may include sludge storage tank 88′ which receives some ofthe settled sludge from SBR 12′ via line 90 and some of the settledsludge from SBR 12″ via line 92 during or after the decant phase in eachrespective SBR 12′, 12″.

System 10′ also includes weighting agent impregnation subsystem 26′which, in this embodiment, is located downstream from sludge storagetank 88′. In this example, impregnation tank 28 and mixer 30 receivessettled sludge from sludge storage tank 88′ by line 100. Impregnationtank 28 also preferably receives virgin weighting agent 33, e.g., fromfeed hopper 34 by line 36, and/or recycled weighting agent 38 fromweighting agent recovery subsystem 74. Mixer 30 mixes the settled sludgeand virgin weighting agent 33 and/or the recycled weighting agent 38 inimpregnation tank 28 to impregnate the weighting agent into thebiological flocs suspended in the settled sludge to form weightedbiological flocs, similarly as discussed with reference to FIG. 1.

System 10′, FIG. 3, also includes weighting agent recovery subsystem 74′which receives the sludge from sludge storage tank 88′. Weighting agentrecovery subsystem 74′ preferably includes separator 78, which in thisembodiment, is located downstream from sludge storage tank 88′ andupstream from weighting agent impregnation subsystem 26. Separator 78recovers the weighting agent from the weighted biological flocs in thesettled sludge in line 95 from sludge storage tank 88′ and reintroduces(recycles) the recovered weighting agent 38 to weighting agentimpregnation subsystem 26 via line 79. Weighting agent recoverysubsystem 74′ may include recovery subsystem 83, FIG. 3, e.g., a wetdrum magnetic separator or similar type device, which is typicallylocated downstream from separator 78.

In one exemplary operation of system 10′, valve 62 is opened and valve64 is closed to fill SBR 12′ (SBR #1) with influent wastewater 14. Thenvalve 62 is closed and valve 64 is opened to fill SBR 12″ (SBR #2).While SBR 12″ is being filled, SBR 12′ undergoes the react, settle, anddecant phases as discussed above. During or after the decant phase inSBR 12′, excess (waste) settled sludge at the bottom of SBR 12′ ispumped to sludge storage tank 88′ via line 90. Some of the settledsludge in sludge storage tank 88 may be directed via line 100 toweighting agent impregnation tank 28 of weighting agent impregnationsubsystem 26′ and some of the sludge in sludge storage tank 88 may bedirected to separator 78 via line 95. Weighting agent impregnationsubsystem 26′ impregnates virgin weighting agent 33 and/or recoveredweighting agent 38 into the biological flocs in the settled sludge inimpregnation tank 28 using mixer 30.

Weighting agent recovery subsystem 74′ then sends the settled sludgehaving weighted biological flocs therein to line 16 via line 76. At thispoint, SBR 12″ (SBR #2) has been filled so valve 62 is opened and valve64 is closed so that the mixture of influent wastewater 14 and thesettled sludge having weighted biological flocs therein is directed tofill SBR 12′ (SBR #1). At this point, SBR 12″ is undergoing the react,settle, and decant phases. Similar, as discussed above, during or afterdecant phase, some of the settled sludge at the bottom of SBR 12″ ispumped to sludge storage tank 88′ via line 92. This settled sludge isprocessed by weighting agent impregnation subsystem 26′ as discussedabove to form weighted biological flocs in the settled sludge inimpregnation mixing tank 28. Weighting agent recovery subsystem 74′ thendirects the settled sludge with the weighted biological flocs therein toline 16, as discussed above. Valve 62 is closed and valve 64 is open tofill SBR 12″ with the mixture of influent wastewater and settled sludgehaving weighted biological flocs. The process of switching between SBR12′ and SBR 12″ continues when ever system 10′ is operational.

Similar as discussed above, the weighted biological flocs introduced tomixed liquor 24 in SBRs 12′, 12″ settle faster to reduce the time neededfor their respective settling phases. This increases the capacity system10′ to treat wastewater and alleviates the problems associated withconventional SBR systems discussed above and provides a cleaner treatedeffluent 50′, 50″.

Similar as discussed above, flocculant 62, FIG. 3, may be added to mixedliquor 24 in SBR 12′, 12″ to enhance settling and thickening of theweighted biological flocs suspended in mixed liquor 24 in SBR 12 andestablishes agglomeration of non-impregnated biological flocs and/orpartially impregnated biological flocs with the weighted biologicalflocs in SBR 12′, 12″. The weighted biological flocs also provide acleaner treated effluent, with fewer suspended solids and relatedcontaminants. Coagulant 64 may also be added to SBR 12′, 12″ forremoving phosphorus from mixed liquor 24 by precipitation and/orcoagulation, as known by those skilled in the art. Mixer 40 and/or airbubbles 18 may be used to maintain biological flocs 23 in suspension inmixed liquor 24 and to mix the flocculant and/or the coagulant withmixed liquor 24 in SBR 12′, 12″.

In another embodiment, weighting agent impregnation subsystem 26′ mayreceive mixed liquor 24 directly from SBR 12′ or directly from SBR 12″.Similar as discussed above with reference to FIG. 1, weighting agentimpregnation tank 28 mixes mixed liquor 24 and virgin weighting agent 33and/or recovered weighting agent 38 from separator 78 and/or recoverysubsystem 83 to impregnate the weighting agent into biological flocssuspended in the mixed liquor to form weighted biological flocs. Theweighted biological flocs are then sent back to SBR 12′ or to SBR 12″.

Thus, system 10′ can impregnate the biological flocs either byimpregnating the biological flocs in the mixed liquor in SBRs 12′, 12″,or by impregnating the biological flocs in the settled sludge output bySBRs 12′, 12″, or using a combination of both methods.

System 10, FIG. 1, and/or system 10′, FIG. 3, may also utilize weightingagent impregnation subsystem 26″, FIG. 4, where like parts have beengiven like numbers. Weighting agent impregnation subsystem 26″ includesventuri mixer/eductor 27 having nozzle 31 and funnel 45 which receivesvirgin weighting agent 33, e.g., from tank 34 by line 36, and/orrecycled weighting agent 38 from separator 78 or recovery subsystem 83,FIGS. 1 and 3. Venturi mixer/eductor 27 preferably receives mixed liquorby line 32, FIG. 1, or settled sludge by line 77, or settled sludge byline 100, FIG. 3. In operation, the velocity of mixed liquor in line 32,FIG. 1, or the settled sludge in line 77, or line 100, FIG. 3, isincreased through nozzle 31, FIG. 4. Virgin weighting agent 33 and/orrecycled weighting agent 38 in funnel 45 enters nozzle 31 by line 39 andtravels downstream to line 37. The widening of line 37 at 41 inducesintimate mixing and entrainment, as shown at 43. This impregnates thevirgin and/or recycled weighting agent into the biological flocs to formweighted biological flocs. The weighted biological flocs are thenreturned to SBR 12, FIG. 1, by line 37, or SBR 12′, 12″; FIG. 3, bylines 76 and 16.

In one design, separator subsystem 78, FIGS. 1 and 3 may be configuredas shear mill 112, FIG. 5A, which shears the sludge in line 76, FIG. 1,or line 95, FIG. 3, to separate the weighting agent from the weightedbiological flocs. Shear mill 112 ideally includes rotor 80 and stator82. In operation, the settled sludge in line 76, FIG. 1 or 95, FIG. 3,enters shear mill 112 and flows in the direction of arrows 180 andenters rotor 80 and then stator 82. Shear mill 112 is designed such thatthere is a close tolerance between rotor 80, FIG. 5B and stator 82, asshown at 93. Rotor 80 is preferably driven at high rotational speeds,e.g., greater than about 1,000 r.p.m., to form a mixture of weightingagent and obliterated flocs in area 181, FIG. 5A, of shear mill 112. Themixture of weighting agent and obliterated flocs exits shear mill 112 byline 79, as shown by arrows 184. FIG. 5C shows in further detail thestructure of one embodiment of shear mill 112. Preferably, rotor 80,FIGS. 5A-5C, and/or stator 82 includes slots which function as acentrifugal pump to draw the settled sludge from above and below rotor80 and stator 82, as shown by paths 182, FIG. 5A, and then hurl thematerials off the slot tips at a very high speed to break the weightedbiological flocs into the mixture of weighting agent and obliteratedflocs. For example, rotor 80, FIG. 5B, may include slots 186, and stator82 may include slots 188. Slots 186 in rotor 80 and/or slots 188 instator 82 are preferably optimized to increase shear energy toefficiently separate the weighting agent from the weighted biologicalflocs. The shear developed by rotor 80 and stator 82 depends on thewidth of slots 186 and 188, the tolerance between rotor 80 and stator82, and the rotor tip speed. The result is shear mill 112 provides ashearing effect which effectively and efficiently separates theweighting agent from the weighted biological flocs to facilitaterecovery of the weighting agent.

In another design, separator subsystem 78, FIGS. 1 and 3, may beconfigured as ultrasonic separator 116, FIG. 6, where like parts havebeen given like numbers. Ultrasonic separator 116 typically includes oneor more ultrasonic transducers, e.g., ultrasonic transducer 262, 264,266, 268, and/or 270, available from Hielscher Ultrasonics GmbH,Stuttgart, Germany, which generates fluctuations of pressure andcavitation in the settled sludge in line 76, FIG. 1 or line 95, FIG. 3.This results in microturbulences that produce a shearing effect tocreate a mixture of weighting agent and obliterated flocs to effectivelyseparate the weighting agent from the weighted biological flocs in thesettled sludge. The resulting mixture of weighting agent and obliteratedflocs exits ultrasonic separator 116 by line 79. In yet another design,separator subsystem 78, FIG. 7, where like parts have been given likenumbers, may be configured as centrifugal separator 118. Centrifugalseparator 114 typically includes cylindrical section 302 located at thetop of hydrocyclone 300 and conical base 304 located below section 302.The settled sludge in line 76, FIG. 1 or line 100, FIG. 3, is fedtangentially into cylindrical section 302 via port 303. Smaller exitport 306 (underflow or reject port) is located at the bottom of conicalsection 304 and larger exit port 308 (overflow or accept port) islocated at the top of cylindrical section 302.

In operation, the centrifugal force created by the tangential feed ofthe sludge by port 303 causes the denser weighting agent to be separatedfrom the biological flocs in the settled sludge. The separated weightingagent is expelled against wall 308 of conical section 304 and exits atport 306. This effectively separates the weighting agent from theweighted biological flocs. The recovered weighting agent 38 exits viaport 306 and may be deposited to weighting agent impregnation system 26,26′, or 26 “, FIGS. 1, 3, and 4. The less dense biological flocs remainin the sludge and exit via port 308 through tube 310 extending slightlyinto the body of the center of centrifugal separator 118.

Although as discussed above, separator subsystem 78 may be configured asa shear mill, an ultrasonic separator, or a centrifugal separator, thisis not a necessary limitation of this invention. In other designs,separator subsystem 78 may be configured as a tubular bowl, a chamberbowl, an imperforate basket, a disk stack separator, and the like, asknown by those skilled in the art.

In the example above where a separator 78, FIGS. 5A-5C, is configured asshear mill 112 to create the mixture of weighting agent and obliteratedbiological flocs, a wet drum magnetic separator or centrifugal separator118, FIG. 7, may be used to recover the weighting agent therefrom e.g.,recycled weighting agent 38, FIGS. 1 and 3, delivered to weighting agentimpregnation subsystem 26 by line 79 and/or recycled weighting agent 38,FIG. 7, delivered to weighting agent impregnation subsystem 26 via port306.

In the example where separator subsystem 78, FIG. 6, is configured as anultrasonic separator 116 to create the mixture of weighting agent andobliterated biological flocs, a wet drum magnetic separator orcentrifugal separator 118, FIG. 7, may be used to recover the weightingagent therefrom, e.g., recycled weighting agent 38, FIGS. 1 and 3,delivered to weighting agent impregnation subsystem 26 by line 79 and/orrecycled weighting agent 38, FIG. 7, delivered to weighting agentimpregnation subsystem 26 via port 306.

The result of recovering and recycling the weighting agent as discussedabove with reference to FIGS. 5A-7 significantly reduces the operatingcosts of wastewater treatment system 10.

System 10, 10′, FIGS. 1 and 3, may also include wasting subsystem 85coupled to separator 78 and/or recovery subsystem 85 which wastes theremaining settled sludge output by separator subsystem 78 and/orrecovery subsystem 83 to control the population of the microorganisms inmixed liquor 24 in SBR 12, FIG. 1, or SBR 12′, 12”, FIG. 3. The capacityof system 10, 10′, FIGS. 1 and 3 to process wastewater 14 may beincreased by increasing the concentration of the mixed liquor suspendedsolids (MLSS) in SBR 12, FIG. 1, or SBR 12′, 12″, FIG. 3, by reducingthe amount of settled sludge wasted by wasting subsystem 85. Increasingthe concentration of the MLSS may reduce the duration of the reactphase. The amount of settled sludge wasted by wasting subsystem 85 mayalso be reduced to increase the concentration of MLSS to enhancenitrification and/or de-nitrification of ammonia in mixed liquor 24. Thenitrification process may also be further enhanced by increasing theamount of dissolved oxygen introduced to SBR 12, 12′, 12″ via bubbles18.

Aside from the preferred embodiment or embodiments disclosed below, thisinvention is capable of other embodiments and of being practiced orbeing carried out in various ways. Thus, it is to be understood that theinvention is not limited in its application to the details ofconstruction and the arrangements of components set forth in thefollowing description or illustrated in the drawings. If only oneembodiment is described herein, the claims hereof are not to be limitedto that embodiment. Moreover, the claims hereof are not to be readrestrictively unless there is clear and convincing evidence manifestinga certain exclusion, restriction, or disclaimer.

Although specific features of the invention are shown in some drawingsand not in others, this is for convenience only as each feature may becombined with any or all of the other features in accordance with theinvention. The words “including”, “comprising”, “having”, and “with” asused herein are to be interpreted broadly and comprehensively and arenot limited to any physical interconnection. Moreover, any embodimentsdisclosed in the subject application are not to be taken as the onlypossible embodiments. Other embodiments will occur to those skilled inthe art and are within the following claims.

In addition, any amendment presented during the prosecution of thepatent application for this patent is not a disclaimer of any claimelement presented in the application as filed: those skilled in the artcannot reasonably be expected to draft a claim that would literallyencompass all possible equivalents, many equivalents will beunforeseeable at the time of the amendment and are beyond a fairinterpretation of what is to be surrendered (if anything), the rationaleunderlying the amendment may bear no more than a tangential relation tomany equivalents, and/or there are many other reasons the applicantcannot be expected to describe certain insubstantial substitutes for anyclaim element amended.

1. A ballasted sequencing batch reactor system for treating wastewatercomprising: one or more sequencing batch reactors; a weighting agentimpregnation subsystem configured to mix biological flocs and weightingagent to form weighted biological flocs; a weighting agent recoverysubsystem configured to recover weighting agent from the weightedbiological flocs and reintroduce the recovered weighting agent to theweighting agent impregnation subsystem.
 2. The system of claim 1 furtherincluding a sludge storage tank configured to receive settled sludgefrom the one or more sequencing batch reactors, store the settled sludgetherein, and regulate the flow of settled sludge to weighting agentrecovery subsystem.
 3. The system of claim 1 in which the weightingagent recovery subsystem includes a separator subsystem for separatingthe weighting agent from the weighted biological flocs.
 4. The system ofclaim 3 in which the separator subsystem includes a shear mill.
 5. Thesystem of claim 3 in which the separator subsystem includes acentrifugal separator.
 6. The system of claim 3 in which the separatorsubsystem includes an ultrasonic separator.
 7. The system of claim 3 inwhich the separator subsystem includes a shear mill and a wet drummagnetic separator.
 8. The system of claim 3 in which the separatorsubsystem includes a shear mill and a centrifugal separator.
 9. Thesystem of claim 3 in which the separator subsystem includes anultrasonic separator and a wet drum magnetic separator.
 10. The systemof claim 3 in which the separator subsystem includes an ultrasonicseparator and a centrifugal separator.
 11. The system of claim 4 inwhich the shear mill includes a rotor and a stator, wherein the rotorand/or the stator include slots sized as to optimize separation ofweighting agent from the weighted biological flocs.
 12. The system ofclaim 1 in which the weighting agent impregnation subsystem includes animpregnation tank and at least one mixer.
 13. The system of claim 1 inwhich the capacity of the system is increased by reducing the durationof a settle phase.
 14. The system of claim 1 in which the one or moresequencing batch reactors are configured to decant clear effluent fromsettled sludge to provide a treated effluent.
 15. The system of claim 14in which the weighted biological flocs enhance the quality of thetreated effluent by reducing the concentration of suspended solids andrelated contaminants therein.
 16. The system of claim 1 furtherincluding a wasting subsystem for wasting settled sludge from theweighting agent recovery subsystem to control a population ofmicroorganisms in a mixed liquor in the one or more sequencing batchreactors.
 17. The system of claim 16 in which the capacity of the systemis increased by increasing the concentration of the mixed liquor in theone or more sequencing batch reactors by reducing the amount of settledsludge wasted by a wasting subsystem.
 18. The system of claim 17 inwhich the capacity of the system is increased by reducing the durationof a react phase.
 19. The system of claim 17 in which the amount ofsettled sludge wasted by the wasting subsystem is reduced to increasethe concentration of mixed liquor suspended solids for enhancingnitrification and/or de-nitrification of ammonia in the mixed liquid.20. The system of claim 19 in which nitrification is enhanced byincreasing the amount of dissolved oxygen introduced into the one ormore sequencing batch reactors.
 21. The system of claim 1 in which acoagulant is added to the one or more sequencing batch reactors forremoving phosphorus by precipitation and/or coagulation.
 22. The systemof claim 1 in which a flocculant is added to the one or more sequencingbatch reactors for enhancing settling and thickening of the weightedbiological flocs and for providing agglomeration of non-impregnatedbiological flocs and/or partially impregnated biological flocs withweighted biological flocs.
 23. The system of claim 1 in which theweighting agent impregnation subsystem includes a venturi mixer/eductor.24. The system of claim 1 in which a majority of the weighting agent hasa particle size less than about 100 μm.
 25. The system of claim 1 inwhich a majority of the weighting agent has a particle size less thanabout 40 μm.
 26. The system of claim 1 in which a majority of theweighting agent has a particle size less than about 20 μm.
 27. Thesystem of claim 1 in which the weighting agent includes magnetite. 28.The system of claim 1 further including a mixer disposed in each of theone or more sequencing batch reactors for maintaining the suspendedsolids or the mixed liquor in suspension.
 29. A method for treatingwastewater using one or more sequencing batch reactors, the methodcomprising: a) receiving influent wastewater in the one or moresequencing batch reactors; b) forming biological flocs in the one ormore sequencing batch reactors; c) impregnating weighting agent into thebiological flocs to form weighted biological flocs; and d) recoveringweighting agent from the weighted biological flocs to reintroduce theweighting agent to step c).
 30. The method of claim 29 further includingthe step of separating the weighting agent from the weighted biologicalflocs.
 31. The method of claim 29 further including the step ofcollecting the weighting agent and recycling the weighting agent to stepc).
 32. The method of claim 29 further including the step of providingweighting agent in which the majority of the weighting agent has aparticle size less than about 100 μm.
 33. The method of claim 29 furtherincluding the step of providing weighting agent in which the majority ofthe weighting agent has a particle size less than about 40 μm.
 34. Themethod of claim 29 further including the step of providing weightingagent in which the majority of the weighting agent has a particle sizeless than about 20 μm.
 35. The method of claim 29 further including thestep of introducing dissolved oxygen to a population of microorganismsto promote growth of biological flocs in a mixed liquor defined by aconcentration of mixed liquor suspended solids.
 36. The method of claim35 further including the step of introducing a flocculant to the mixedliquor to enhance settling and thickening of the weighted biologicalflocs and to establish agglomeration of non-impregnated biological flocsand/or partially impregnated biological flocs with the weightedbiological flocs.
 37. The method of claim 35 further including the stepof separating and collecting the weighted biological flocs from themixed liquor in the one or more sequencing batch reactors to provide asecondary effluent and a settled sludge.
 38. The method of claim 37further including the step of recycling the majority of the settledsludge to step b).
 39. The method of claim 37 further including the stepof decanting the clean effluent from the settled sludge in the one ormore sequencing batch reactors to provide a treated effluent.
 40. Themethod of claim 37 further including the step of wasting the remainingsettled sludge using a wasting subsystem to control the population ofthe microorganisms in the mixed liquor.
 41. The method of claim 29further including the step of increasing the capacity of the system byreducing the duration of a settle phase.
 42. The method of claim 39further including the step of enhancing the quality of the treatedeffluent by reducing the concentration of suspended solids and relatedcontaminants therein.
 43. The method of claim 27 further including thestep of wasting settled sludge from the weighting agent recoverysubsystem to control a population of microorganisms in a mixed liquor inthe one or more sequencing batch reactors.
 44. The method of claim 43further including the step of increasing the capacity of the system byincreasing the concentration of the mixed liquor in the one or moresequencing batch reactors by reducing the amount of settled sludgewasted by a wasting subsystem.
 45. The method of claim 44 furtherincluding the step of increasing the capacity of the system by reducingthe duration of a react phase.
 46. The method of claim 43 furtherincluding the step of reducing the amount of settled sludge wasted bythe wasting subsystem to increase the concentration of mixed liquorsuspended solids which enhances nitrification and/or de-nitrification ofammonia in the mixed liquid.
 47. The method of claim 35 furtherincluding the step of enhancing nitrification by increasing the amountof dissolved oxygen introduced into the one or more sequencing batchreactors.
 48. The method of claim 29 in which the weighting agent isimpregnated into the biological flocs in step b) by mixing the mixedliquor and the biological flocs at a predetermined energy level.